1. Field of the Invention
The present invention generally relates to a wheel support bearing assembly having a built-in magnetic encoder and, more particularly, to a protective cap employed in the wheel support bearing assembly for protecting the magnetic encoder.
2. Description of the Prior Art
Automotive vehicles equipped with an anti-skid braking system (ABS) generally includes a rotation detecting device for detecting the number of revolutions of at least one vehicle wheel so that the anti-skid braking system can be controlled to minimize the hazard of the automotive vehicle being skidded. The rotation detecting device is generally incorporated in a wheel support bearing assembly. The wheel support bearing assembly having the rotation detecting device incorporated therein is suggested in, for example, the Japanese Laid-open Patent Publication No. 2001-215132 and includes an inner member, an outer member positioned radially outwardly of the inner race with an annular working space defined between it and the inner race, circumferentially extending rows of rolling elements rollingly accommodated within the annular working space, a sealing member for sealing each of opposite open ends of the annular working space, and a magnetic encoder integrated with one of the sealing members and having a plurality of alternating magnetic poles deployed in a direction circumferentially of any one of the inner and outer races. The rotation detecting device referred to above is constructed of the magnetic encoder in combination with a sensor positioned in face-to-face relation with the magnetic encoder for detecting change in magnetic polarity as a result of rotation of the vehicle wheel.
However, it has been found that since in the wheel support bearing assembly of the structure discussed above, the magnetic encoder built therein is exposed or unprotected when the wheel support bearing assembly is coupled with a knuckle connected with a vehicle body structure, metallic particles such as fine metallic shavings remained on, for example, the knuckle are deposited on and/or stick to the magnetic encoder, lowering the performance of the magnetic encoder. As is well known to those skilled in the art, the knuckle is in most cases wetted with oil and, therefore, fine metallic shavings removed from the knuckle as a result of grinding are deposited on the knuckle in contact with the oil. When the wheel support bearing assembly is coupled with the contaminated knuckle, the magnetic encoder incorporated in the wheel support bearing assembly is susceptible to deposition of the metallic particles. Accordingly, the workshop requires a smearing process to remove the magnetic particles deposited on the magnetic encoder.
Not only when the wheel support bearing assembly is being coupled with the knuckle, but also when, for example, the wheel support bearing assembly is being transported, there is a high possibility that the metallic particles may deposit on the magnetic encoder.